1. Field of the Invention
The present invention relates to a method of forming trenches in an SOI substrate.
2. Description of the Related Art
Methods of forming trenches are known in which trenches are formed by anisotropic dry etching in an SOI (Silicon On Insulator) substrate in which an oxide film insulating layer and a silicon semiconductor layer are laid one over another on a silicon support substrate. This etching is performed by etching the silicon semiconductor substrate from its surface through the plasma action of an etching gas. A mixed gas containing fluorine-containing gas and oxygen gas, for example, is used as the etching gas. For example, Japanese Patent Kokai No. 2006-93269 (Patent literature 1) discloses an etching method including a first etching step of forming a tapered opening in a silicon semiconductor layer using a first etching gas containing fluorine-containing gas and O2 and a second etching step of performing etching through the tapered opening using a second etching gas containing fluorine-containing gas, O2, and HBr.